I don't think this is firmware related but sensor hardware architecture related.
1) This kind of sensors with multiple raw sizes like for example 7D, 5D mark II, 5D mark III used to have, do not exist anymore. Except the recent cameras like 6D mark II for example, that still use old sensors (single gain), this camera still have multiple raw resolutions, but worse dynamic range.
Since they added dual gain to sensors (since 1D X mark II), multiple resolutions in RAW mode have disappeared.
So until this moment you either have multiple raw resolution or better dynamic range, you cannot have both.
2) Also confirmed by electron microscopy analysis of a single gain sensor (1D X)
Source of knowledge Engineering and information technology.
eng-info-tech.blogspot.com
"additional transistor connecting FD in three rows is used for binning"
3) The resolution of raw video mode of cameras like R5 is only in the 8K mode not also in 4K mode. The 8K mode is a 1:1 pixel read of the sensor at 16:9 aspect ratio, so there are only some skipped rows at the botton and top of the sensor, there is no binning involved.
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But is still possible to have good multiple resolutions in JPEG mode, this is good enough for sport photographers. For example Sony A1 (50Mpx) can shot JPEG at 21 and 12 Mpx. Canon R5 (45Mpx) can shot JPEG at 22, 12 and 4 Mpx.